A rim for a bicycle wheel has a structure that extends between two opposite sides, connected by one or more bridges to form a U-shaped, inverted A-shaped or more complex section, with a plurality of chambers. In wheels with pad brakes, generally on the left and right sides of the rim, braking positions are formed on the rim where the brake pads are to be pressed to brake the bicycle.
The extensive search for lightness in bicycle wheels has led to rims being made with ever lower thicknesses. In extreme cases, there is a bearing structure of the rim that is only a little more than sufficient to withstand the loads to which it is subjected. As a result of this, the rim wear caused by brake pad rubbing must be watched carefully. Excessive rim wear at the braking surfaces is unsafe, since it can lead to the rim suddenly collapsing in dangerous situations requiring very hard braking. Therefore, it is necessary to indicate the rim's wear level so a cyclist knows when to replace the rim.
Rims made from metallic material comprise annular or pointed recesses formed on the braking surfaces. The depth of the recess decreases with wear. When the recess disappears, the cyclist must replace the rim. Annular recesses are easy to make during extrusion of semi-worked product from which the rim is formed or by machining. Pointed recesses, on the other hand, are made by machining or by upsetting.
For rims made from composite material, typically made with structural fibers in a matrix of polymeric material, it is not possible to make the recesses by extrusion or upsetting and machining the recesses would shear the structural fibers and weaken the rim.
Consequently, the present invention concerns a rim for a bicycle and a bicycle wheel made from composite material.